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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorKBabs
    • CommentTimeOct 3rd 2018 edited
     
    Hello all,

    I am soon to start the renovation of a solid wall, 1930's detached house. The work will also include the addition of a large extension - side and rear, double storey.

    As the existing part of the house is not insulated, I will be opting for EWI (EPS grey). A decision has not yet been made with regards to how the extension walls are built. I am keen for the finished house to be (within economical reason) warm and reasonably cheap to heat. The original plan was for the extension walls to be 300mm cavity. I don't have a problem with that, however, concerns are, cold bridging from old to new, plus around steel work. As the house needs to be rendered anyway, I was going to wrap an additional (say) 50mm of EPS around the new walls - it won't cost too much extra, so what the heck. I was hoping this would make the house more airtight and warmer etc etc.

    Another option is to build the extension from solid block work and EWI the house house. I can easily to this to current building regs, but my worry is that from a thermal POV, it doesn't go far enough.

    3 things on my mind:

    1 - Is Cavity + EWI a good idea to increase U value or would I be better off building walls solid and using a thicker EPS board? I worry just how thick it will need to be!

    2 - Will a well wrapped EWI wall be a much better job than a builder 'chucking in' 100mm batts in a cavity - assuming both are to building regs standard?

    3 - Whatever the method above, how is the improvement (beyond current building regs) felt when the numbers are so small, ie, .3 U value to .2 etc. - is it really worth it?

    Your answers / views are most welcome and appreciated.

    Best regards,

    Keith
  1.  
    Welcome.

    Building insulated cavity an then putting a little bit of EWI over seems to be just making work for yourself. Lots of threads on here about single skin and EWI. Re your Q.3 - I would argue that any improvement in U value really helps, but building 'solid' may just allow you to get everything more airtight.

    As to Q.2, the answer is - yes, if it's done properly. It's possible to achieve a standard akin to 'chucking in' cavity insulation with EWI!

    I have really struggled to find an EWI contractor who will do every element of it to the standard I require. Still have not done so!

    I may just be unlucky in my area.
    • CommentAuthorKBabs
    • CommentTimeOct 3rd 2018 edited
     
    " As to Q.2, the answer is - yes, if it's done properly. It's possible to achieve a standard akin to 'chucking in' cavity insulation with EWI! "

    Do you mean if it is done in a careless way?

    The guy I have lined up to do the EWI seems very conscientious and I trust him to do a good job.
    •  
      CommentAuthordjh
    • CommentTimeOct 3rd 2018
     
    Posted By: KBabs1 - Is Cavity + EWI a good idea to increase U value or would I be better off building walls solid and using a thicker EPS board? I worry just how thick it will need to be!

    Building a solid wall and EPS is simpler. EPS up to 200 mm is fairly common, and 300 mm is available.

    2 - Will a well wrapped EWI wall be a much better job than a builder 'chucking in' 100mm batts in a cavity - assuming both are to building regs standard?

    Probably; it does depend on the builder.

    3 - Whatever the method above, how is the improvement (beyond current building regs) felt when the numbers are so small, ie, .3 U value to .2 etc. - is it really worth it?

    It's best not to think about the smallness of the numbers; think instead about ratios like 0.2/0.3 as percentages. As well as insulation, you also need to think about airtightness, and consequent on that you need to think about ventilation. If you do then the benefits are to your comfort as well as to your pocket.
  2.  
    ''Do you mean if it is done in a careless way?''

    Yes. That way seems to be quite common! Well done, you, for finding a good contractor. whereabouts in the UK are you?
    • CommentAuthorKBabs
    • CommentTimeOct 3rd 2018
     
    " It's best not to think about the smallness of the numbers; think instead about ratios like 0.2/0.3 as percentages. As well as insulation, you also need to think about airtightness, and consequent on that you need to think about ventilation. If you do then the benefits are to your comfort as well as to your pocket."

    I'm assuming that solid wall and EWI by definition will give you a more air tight house? In terms of ventilation, I was planning on installing something like this...

    https://www.envirovent.com/home-ventilation/products/whole-house-ventilation-systems/mr-venty-eco-sub-2-sub-twin/

    Having used one before, I found the product excellent at dealing with high humidity, ie. we got no condensation!
    • CommentAuthorKBabs
    • CommentTimeOct 3rd 2018
     
    <blockquote><cite>Posted By: Nick Parsons</cite>''Do you mean if it is done in a careless way?''

    Yes. That way seems to be quite common! Well done, you, for finding a good contractor. whereabouts in the UK are you?</blockquote>

    I meant to say conscientious, btw! We live in Billericay, Essex.
    • CommentAuthorKBabs
    • CommentTimeOct 4th 2018 edited
     
    <blockquote><cite>Posted By: Nick Parsons</cite>''Do you mean if it is done in a careless way?''

    Yes. That way seems to be quite common! Well done, you, for finding a good contractor. whereabouts in the UK are you?</blockquote>

    Does this relate more to the quality of the block work, installation of EWI, or combination of both?
  3.  
    Application of the EWI. In my experience the most frequent placation I have had, or heard, is that the odd gap does not matter, as it'll all be covered with 2 nice coats of render, so you won't see them!:sad:
    • CommentAuthorKBabs
    • CommentTimeOct 9th 2018 edited
     
    If building solid/ewi, will using an aerated block mean rooms warm quieter, whereas a medium dense block will be slower to warm up time but will have better (thermal) mass?

    Thanks for all you helpful responses.
    • CommentAuthorjfb
    • CommentTimeOct 9th 2018
     
    I don't think you would want to be building a single skin wall out of an aerated block - medium dense block much stronger. This isn't based on actual knowledge of regs/structural calks but just my gut feeling. I'm sure someone else will have more info.

    And yes I think you are right regarding warm up times and thermal mass.
    • CommentAuthorgoodevans
    • CommentTimeOct 9th 2018
     
    Posted By: jfbI don't think you would want to be building a single skin wall out of an aerated block


    Also a lightweight wall may let more sound in. - I would get as much mass in the wall as the foundations/builders can take/lift.
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